Cu-BASED SINTERED SLIDING MEMBER

ABSTRACT

A Cu-based sintered sliding member that can be used under high-load conditions. The sliding member is age-hardened, including 5 to 30 mass % Ni, 5 to 20 mass % Sn, 0.1 to 1.2 mass % P, and the rest including Cu and unavoidable impurities. In the sliding member, an alloy phase containing higher concentrations of Ni, P and Sn than their average concentrations in the whole part of the sliding member, is allowed to be present in a grain boundary of a metallic texture, thereby achieving excellent wear resistance. Hence, without needing expensive hard particles, there can be obtained, at low cost, a Cu-based sintered sliding member usable under high-load conditions. Even more excellent wear resistance is achieved by containing 0.3 to 10 mass % of at least one solid lubricant selected from among graphite, graphite fluoride, molybdenum disulfide, tungsten disulfide, boron nitride, calcium fluoride, talc and magnesium silicate mineral powders.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C.§371 of International Patent Application No. PCT/JP2010/064565, filedAug. 27, 2010, and claims the benefit of Japanese Patent Application No.2009-201072, filed Aug. 31, 2009, all of which are incorporated byreference herein. The International Application was published inJapanese on Mar. 3, 2011 as International Publication No. WO 2011/024941under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to a Cu-based sintered sliding member,particularly to a Cu-based sintered sliding member compatible with useunder high load conditions.

BACKGROUND OF THE INVENTION

As for bearings used for an automobile, an expensive ball bearing isused for high load applications, such as a bearing for an ABS system ofan automobile, while an inexpensive Fe—Cu-based sintered bearing is usedfor a motor system of an automobile wiper or the like. Due to reductionin size of the motor system, however, the bearing for the motor systemis also progressively reduced in size to thereby increase a load appliedto the bearing parts. Therefore, ever more excellent performances inwear resistance and seizure resistance are required for the bearingparts.

Recently, to meet strong demands for cost reduction from the market,employing an inexpensive sintered bearing instead of an expensive ballbearing is under consideration even for high load applications such asthe foregoing ABS system of the automobile. When using the conventionalCu-based sintered sliding member, however, a load applied thereto is tooheavy for it and hence the load exceeds its allowable load range, thusmaking it impossible to use the member. Further, Fe—Cu based sinteredsliding members whose hardness and strength are higher than those of theCu-based sintered sliding members contain Fe, while a shaft borne by theCu-based sintered sliding member is also made of an Fe-based metal, andthus, abnormal friction and seizure are likely to occur due to thesame-metal phenomenon, even though the probability of the occurrencethereof is low, thus leading to the problem that the reliability thereofas a sliding member is insufficient. Thus, a Cu-based sintered slidingmember which is less expensive than the expensive ball bearings and iscapable of being used under higher load conditions than in the past hasbeen sought after.

As a conventional art with respect to the Cu-based sintered slidingmember usable under high load conditions, there is disclosed a Cu-basedsintered sliding member (in e.g., Japanese unexamined patent applicationpublication No. H5-195117) having excellent wear resistance and seizureresistance under high-temperature, high-load and poor-lubricationconditions when it is used for a valve guide or the like of aninternal-combustion engine.

The Cu-based sintered alloy according to the conventional art is aCu—Ni—Sn based alloy whose composition gives rise to a spinodaldecomposition through an aging treatment. By undergoing the spinodaldecomposition, the Cu—Ni—Sn based alloy is allowed to be formed with amicrostructure to thereby strengthen its metallic substrate. Further,through the addition of Ni-based hard particles having excellentadhesiveness to the metallic substrate along with MoS₂ as a solidlubricant, wear resistance and seizure resistance are imparted theretounder high-temperature, high-load and poor-lubrication conditions.

The Ni-based hard particles used in the conventional art, however, arenot only expensive but a vacuum sintering process is required thereforas Cr is contained in the Ni-based hard particles, thus leading to highmanufacturing cost, resulting in an insufficient cost advantage.

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Therefore, it is an object of the present invention to provide a Cu-basesintered sliding member which eliminates the need for the addition ofexpensive hard particles and is capable of being used under high loadconditions.

Means for Solving the Problem

A first aspect of the present invention is a Cu-based sintered slidingmember, age-hardened and including:

5 to 30% by mass of Ni;

5 to 20% by mass of Sn;

0.1 to 1.2% by mass of P; and

the rest including Cu and unavoidable impurities,

wherein said Cu-based sintered sliding member includes an alloy phasepresent in a grain boundary of a metallic texture, the alloy phaseincluding higher concentrations of Ni, P and Sn than averageconcentrations of Ni, P and Sn in the whole sliding member.

A second aspect the present invention is the Cu-based sintered slidingmember according to the first aspect, further including 0.3 to 10% bymass of at least one, serving as a solid lubricant, selected from amonggraphite, graphite fluoride, molybdenum disulfide, tungsten disulfide,boron nitride, calcium fluoride, talc and magnesium silicate mineralpowders.

Effects of the Invention

According to the constitution described above, by adding P to theCu—Ni—Sn based alloy while utilizing a property of the Cu—Ni—Sn basedalloy giving rise to hardening by aging treatment, strength of the alloymetallic substrate is further increased, and at the same time, theNi—P—Cu—Sn alloy phase whose concentration of each of Ni, P and Sn ishigher than that of the metallic substrate is allowed to be present inthe grain boundary. As a result, there can be obtained the Cu-basedsintered sliding member having excellent wear resistance, realizinglow-cost production due to no need of the expensive hard particles, andcapable of being used under the high-load condition of a bearing used.

Further, addition of the solid lubricant permits the wear resistance tobe improved. The solid lubricant may contain one or more substancesselected from among graphite, graphite fluoride, molybdenum disulfide,tungsten disulfide, boron nitride, calcium fluoride, talc (Mg₃SiO₄(OH)₂)and magnesium silicate (MgSiO₃) mineral powders.

BRIEF DESCRIPTION OF THE DRAWING

These and other features and advantages of the present invention willbecome more readily appreciated when considered in connection with thefollowing detailed description and appended drawing, wherein likedesignations denote like elements in the various views, and wherein:

FIG. 1 is an electron microscope photograph illustrating an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION Mode for Carrying Out theInvention

Preferred embodiments of the present invention are described in detailwith reference to the accompanying drawings. The hereinbelow-describedembodiments shall not be construed as limiting the subject matter of thepresent invention set forth in claims. Further, not all featuresdescribed hereunder are essential requirements of the present invention.In each embodiment, a novel Cu-based sintered sliding member differentfrom the conventional ones is employed so that there can be obtained anunprecedented Cu-based sintered sliding member, the description of whichwill be given hereinbelow, respectively.

According to the present invention, while taking advantage of such aproperty of the Cu—Ni—Sn based alloy that it gives rise to hardening byan aging treatment, the alloy metallic substrate is further increased instrength by adding P thereto, and the Ni—P—Cu—Sn alloy phase havinghigher concentrations of Ni, P and Sn than the metallic substrate isallowed to be present in the grain boundary, thus enabling the excellentwear resistance to be obtained, eliminating the need for the expensivehard particles and thus leading to low cost, whereby there can beobtained the Cu-based sintered sliding member that is capable of beingused under the high load usage environment of bearings. Furthermore,adding the solid lubricant agent enable the wear resistance to beimproved. As to the property of the Cu—Ni—Sn based alloy giving rise tohardening by an aging treatment, it is known that within a givencomposition range, Ni and Sn are dissolved in Cu to form a singlealpha-phase structure, thus giving rise to a spinodal hardening by anaging treatment. Here, the wording, spinodal hardening, means suchphenomenon that due to a structure produced by spinodal decompositionhaving a periodic structure on the order of several nanometers tothereby form an extremely fine structure, deformation resistanceincreases by an increase in strain energy or the like, therebyincreasing hardness or strength.

Next, a description is given of the reason why the composition of asintered Cu alloy that constitutes the Cu-based sintered sliding memberof the present invention is to be limited.

(a) Ni: 5 to 30% by Mass

Ni, together with P, Sn and Cu, forms a solid solution of a metallicsubstrate to improve the strength of a sintered alloy by age hardening.Further, an alloy phase whose Ni, P and Sn concentrations are higherthan those of the metallic substrate is allowed to be present in thegrain boundary, thereby contributing to improving wear resistance. Anamount of Ni required for the hardening by aging treatment is at least5% by mass, while if more than 30% by mass of Ni is added, there isrecognized no improvement of hardness attributable to the agingtreatment, thus undesirably leading to the opposite effect of anincreased raw material cost.

(b) Sn: 5 to 20% by Mass

Sn, together with Ni, P and Cu, forms the solid solution of the metallicsubstrate to improve the strength of a sintered alloy by age hardening.Further, the alloy phase whose Ni, P and Sn concentrations are higherthan those of the metallic substrate is allowed to be present in thegrain boundary, thereby contributing to improving wear resistance. Anamount of Sn required for the hardening by aging treatment is at least5% by mass and if more than 20% by mass of Sn is added, there isrecognized no improvement of hardness attributable to the agingtreatment, thus undesirably leading to the opposite effect of anincreased wearing aggressiveness to other materials.

(c) P: 0.1 to 1.2% by Mass

P improves sintering performance and forms, together with Ni, Sn and Cu,the solid solution of the metallic substrate to improve the strength ofa sintered alloy. Further, the alloy phase whose Ni, P and Snconcentrations are higher than those of the metallic substrate isallowed to be present in the grain boundary, thereby contributing toimproving wear resistance. When the content of P is less than 0.1% bymass, a predetermined wear resistance cannot be obtained. Contrarily,when the content of P exceeds 1.2% by mass, wearing aggressiveness to asliding counterpart member is increased, thus undesirably wearing thesame.

(d) Solid Lubricant: 0.3 to 10% by Mass

The solid lubricant may contain 0.3 to 10% by mass of at least one ofgraphite, graphite fluoride, molybdenum disulfide, tungsten disulfide,boron nitride, calcium fluoride, talc (Mg₃SiO₄(OH)₂) and magnesiumsilicate (MgSiO₃) mineral powders. When the content of the solidlubricant is less than 0.3% by mass, the improvement in wear resistancecannot be obtained. Contrarily, when the content of the solid lubricantexceeds 10% by mass, its strength noticeably decreases, and thus it isnot desirable.

Here, graphite and graphite fluoride are present as free graphite andfree graphite fluoride dispersed in the metallic substrate, and impartan excellent lubricating property to a sintered alloy to therebycontribute to the improvement in wear resistance of the sintered alloy.Further, molybdenum disulfide, tungsten disulfide, boron nitride,calcium fluoride, talc (Mg₃SiO₄(OH)₂) and magnesium silicate (MgSiO₃)mineral powders serve to impart an excellent lubricating property to thesintered alloy and to lessen the chance of metal contact between slidingmembers, thus contributing to the improvement in wear resistance of thesintered alloy. In addition, talc becomes enstatite after sintering.

Embodiment 1

Next is a description of embodiments with reference to an appendeddrawing.

In manufacturing the sintered alloy, raw powders are filled in a mold ofa required shape and are subjected to powder compacting, thus obtaininga compact with a required density. This compact is sintered in areductive atmosphere to obtain a sintered alloy. Then, this sinteredalloy is subjected to a sizing process to satisfy the requireddimensional accuracy using a mold. The size, density, hardness andstrength of the sintered alloy after the sizing process are tested toselect, as products, ones which have passed the test. Examples of suchproducts include a bearing acting as a sliding member.

Experimental Examples

As raw powders, there were prepared electrolytic Cu powders with 100mesh diameter, Sn atomized powders with 250 mesh diameter, Cu-basedatomized powders including 8% by mass of P with 200 mesh diameter,Cu-based atomized powders including 30% by mass of Ni with 250 meshdiameter, while as additive solid lubricants, there were preparedgraphite powders with 20 μm average diameter, molybdenum disulfidepowders with less than 150 μm average diameter, calcium fluoride powderswith 60 μm average diameter, and talc powders with 20 μm averagediameter.

These raw powders were mixed so as to have the final compositions shownin Table 1 and Table 2, to which were added 0.5% by mass of zincstearate and then mixed together for 20 minutes using a V-type mixer.Thereafter, pressure molding was applied to the mixed compound at agiven pressure within 200 to 300 MPa to produce green compacts, Then,these green compacts were sintered at a given temperature within a rangeof 840 to 940 degrees C. in an atmosphere of an endothermic gas obtainedby mixing a natural gas and an air and allowing the same to pass througha heated catalyst to thereby be decomposed and denatured, and then theywere subjected to a sizing process, and to an aging treatment for 1 hourin a non-oxidizing atmosphere at a given temperature within 350 to 450degrees C., followed by impregnating a Cu-based sintered sliding memberthus produced with a synthetic oil, whereby ring-shaped test pieces ofCu-based sintered sliding members were produced, said test pieces eachhaving a size of 18 mm outer diameter, 8 mm inner diameter and 8 mmheight, and including: a Cu-based sintered sliding member with theingredient composition shown in Table 1 (hereunder, referred to as anexample of the present invention), and for comparison purpose, aCu-based sintered sliding member with P removed therefrom and a Cu-basedsintered sliding member with an ingredient composition departing fromthat of the example of the present invention (hereunder, referred to ascomparative examples). Note that the Cu-based sintered sliding membersthus obtained had air holes distributed in their metallic substrates ina proportion of 5 to 25% by mass.

The following tests were performed using the ring-shaped test piecesincluding Cu-based sintered sliding members 1 to 13 of the presentinvention (hereunder, referred to as examples 1 to 13 of the presentinvention), Cu-based sintered sliding members 1 to 13 for comparisonpurpose (hereunder, referred to as comparative examples 1 to 13), andconventional examples 1, 2 including a Cu-based sintered sliding membersubjected to no age hardening and a Fe—Cu-based sintered sliding member.The results of radial crushing tests and wear resistance tests are shownin Tables 1 and 2.

Here, Table 1 shows the examples 1 to 4 of the present invention, thecomparative examples 1 to 8, and the conventional examples 1 to 2, whileTable 2 shows the examples 5 to 13 of the present invention, and thecomparative examples 9 to 13.

Radial Crushing Test:

Load was applied radially to each of the ring-shaped test piecesincluding the examples 1 to 13 of the present invention, the comparativeexamples 1 to 13, and the conventional examples 1 to 2. Then, the loadsapplied to the rings at the moment the ring-shaped test pieces werebroken were measured to calculate the strengths thereof. The strengthscalculated are shown in a column labeled as “radial crushing strength”in Tables 1, 2.

Wear Resistance Test:

A shaft made of S45C steel was inserted into each of the ring-shapedtest pieces including the examples 1 to 13 of the present invention, thecomparative examples 1 to 13, and the conventional examples 1 to 2.Then, the test was performed in such a manner that the shaft was rotatedat a speed of 75 m/min for 1,000 hours with a load being applied fromthe outside of the ring-shaped test piece so that the pressure to thesurface of the test piece became 1.5 MPa in the radial direction (in thedirection perpendicular to the axial direction of the shaft). Themaximum abrasion depths after the tests on the respective slidingsurfaces of the ring-shaped test pieces and the shafts made of SC45 weremeasured to evaluate wear resistance. The test results are depicted inTables 1, 2.

Note that the conditions under which the present wear resistance testswere performed were determined on the assumption of high-loadconditions.

TABLE 1 Physical Properties after Aging Treatment Maximum Radial MaximumAbrasion With or Ingredient Composition (mass %) Crushing HardnessAbrasion Depth of Shaft Without Age Ni Sn P Cu Strength(N/mm²) (Hv5)Depth (mm) Material (mm) Hardening Examples of 1 9 8 0.3 the Rest 618145 0.007 0.002 With the Present 2 7 7 0.3 the Rest 538 136 0.012 <0.001With Invention 3 12  13  0.3 the Rest 654 158 0.006 0.002 With 4 25  17 0.4 the Rest 710 172 0.005 0.003 With Comparative 1 8 7 0*  the Rest 491127 0.027 0.002 With Examples 2 7 7 0*  the Rest 426 115 0.032 <0.001With 3 12  13  0*  the Rest 511 132 0.022 0.001 With 4 12  10   1.4* theRest 566 174 0.005 0.023 With 5  4* 2 0.2 the Rest 333 51 0.097 0.001With 6 32* 19  1.0 the Rest 583 146 0.020 0.007 With 7 5  1* 0.2 theRest 347 49 0.104 0.001 With 8 25  22* 0.5 the Rest 605 149 0.008 0.021With Conven- 1 Cu—9%Sn—0.8%C—0.3%P 300 60 0.136⁺⁺ 0.001⁺⁺ Without tional2 Fe—20%Cu—2%C 400 95 0.020 0.045 Without Examples (In the table, a *mark indicates the figure is outside the scope of the present inventionand a ⁺⁺ mark indicates measured data after 100 test hours.)

TABLE 2 Physical Properties after Aging Treatment Maximum Radial MaximumAbrasion Ingredient Composition (mass %) Crushing Hardness AbrasionDepth of Shaft Ni Sn P C MoS₂ CaF₂ MgSiO₃ Cu Strength(N/mm²) (Hv5) Depth(mm) Material (mm) Examples of 5 10 7 0.3 2 0 0 0 the Rest 536 106 0.002<0.001 the Present 6 7 8 0.3 0 2 0 0 the Rest 553 110 0.003 <0.001Invention 7 9 7 0.4 0 0 2 0 the Rest 566 121 0.004 0.001 8 8 8 0.3 0 0 02 the Rest 540 109 0.004 0.001 9 6 6 0.3 1 0 0 0 the Rest 502 102 0.007<0.001 10 15 13 0.7 5 0 0 0 the Rest 711 154 0.002 <0.001 11 17 15 0.9 70 0 0 the Rest 697 174 0.002 <0.001 12 20 13.5 0.5 2 0 0 0 the Rest 669158 0.004 <0.001 13 28 18 1.1 1 1 1 1 the Rest 645 167 0.006 0.001Comparative 9 10 10 0*  2 0 0 0 the Rest 405 91 0.018 <0.001 Examples 109 7 0.8 11* 0 0 0 the Rest 255 48 0.038 <0.001 11 10 9 0.3 0 12* 0 0 theRest 223 44 0.064 <0.001 12 10 9 0.3 0 0 11* 0 the Rest 188 32 0.1080.010 13 12 10  1.4* 0 0 0 11* the Rest 159 35 0.135 0.012 (In thetable, a * mark indicates the figure is outside the scope of the presentinvention.)

The results shown in Tables 1, 2 indicate that the maximum abrasiondepths in the ring-shaped test pieces according to the examples of thepresent invention were smaller than those in the ring-shaped test piecesincluding the comparative examples and the conventional examples. Hence,it is learnt that the ring-shaped test pieces according to the presentinvention have excellent wear resistance. On the other hand, it islearnt from the comparative examples 1 to 13 whose ingredientcompositions depart from the scope of the present invention that thering-shaped test pieces according to the comparative examples 1 to 13are inferior in respect of at least one characteristic from amongstrength, wear resistance and wearing aggressiveness to shaft. Table 1shows that the comparative examples 1 to 3 including less than 0.1% bymass of P had larger maximum abrasion depths than the examples of thepresent invention, while the comparative example 4 including more than1.2% by mass of P had larger maximum abrasion depths of the counterpartshaft material as compared to the examples of the present invention; thecomparative example 5 including less than 5% by mass of Ni had largermaximum abrasion depths as compared to the examples of the presentinvention, while the comparative example 6 including more than 30% bymass of Ni had larger maximum abrasion depths as well as larger maximumabrasion depths of the counterpart shaft material as compared to theexamples of the present invention; and the comparative example 7including less than 5% by mass of Sn had larger maximum abrasion depthsas compared to the examples of the present invention, while thecomparative example 8 including more than 20% by mass of Sn had largermaximum abrasion depths of the counterpart shaft material as compared tothe examples of the present invention. Further, it is shown that thecomparative examples 1, 2, 3, 5 and 7 had inferior radial crushingstrength as compared to the examples of the present invention.

Table 2 shows that the comparative example 9 including less than 0.1% bymass of P, the comparative examples 10 to 12 including more than 10% bymass of the solid lubricant, and the comparative example 13 includingmore than 10% by mass of the solid lubricant as well as more than 1.2%by mass of P, had inferior radial crushing strength as well as largermaximum abrasion depths, as compared to the examples of the presentinvention.

The alloy of the example 1 of the present invention was analyzed todetermine Ni, P, Sn and Cu within the alloy phase in which theconcentration of each of Ni, P and Sn present in the grain boundary ofthe metallic texture was higher than the average concentration thereofin the whole alloy, using an electron-beam microanalyzer (EPMA). Theresult obtained is shown in Table 3. An electron microscope photograph(COMPO image) is shown in FIG. 1 as one example of the alloy phase thusanalyzed.

TABLE 3 Analytical Value (wt %) Ni P Sn Cu Example 1 of the PresentInvention 64.342 10.820 14.057 9.995 Alloy Phase in Grain Boundary

With an EPMA analytical condition set at the acceleration voltage of 15KV and the beam diameter φ of 1 μm, the alloy phase in the grainboundary shown in FIG. 1 was measured at five places. The average valuefor each metal is shown in Table 3. It is noted from the analysis resultthat the alloy of the example 1 of the present invention included thespecific alloy phase present in the grain boundary, said specific alloyphase including higher Ni, P and Sn concentrations than the averageconcentrations thereof in the whole sintered alloy.

In addition, the present invention is not limited to the foregoingembodiments and various modifications are possible. For example, whilstthe bearing, acting as a sliding member, having a sliding surface in itsinner circumferential surface, is described as an example of the presentinvention in the foregoing embodiments, the Cu-based sintered slidingmember according to present invention may be applicable to other slidingmembers having sliding surfaces.

1. A Cu-based sintered sliding member that is age-hardened, said slidingmember comprising: 5 to 30% by mass of Ni; 5 to 20% by mass of Sn; 0.1to 1.2% by mass of P; and the rest including Cu and unavoidableimpurities, wherein said Cu-based sintered sliding member comprises analloy phase present in a grain boundary of a metallic texture, saidalloy phase including higher concentrations of Ni, P and Sn than averageconcentrations of Ni, P and Sn in the whole sliding member.
 2. TheCu-based sintered sliding member according to claim 1, furthercomprising 0.3 to 10% by mass of at least one solid lubricant selectedfrom among graphite, graphite fluoride, molybdenum disulfide, tungstendisulfide, boron nitride, calcium fluoride, talc and magnesium silicatemineral powders.
 3. The Cu-based sintered sliding member according toclaim 1, further comprising 0.3 to 10% by mass of at least one solidlubricant selected from graphite and graphite fluoride.
 4. The Cu-basedsintered sliding member according to claim 1, further comprising 0.3 to10% by mass of at least one solid lubricant selected from amongmolybdenum disulfide, tungsten disulfide, boron nitride, calciumfluoride, talc and magnesium silicate mineral powders.
 5. The Cu-basedsintered sliding member according to claim 2, wherein at least one solidlubricant is selected from graphite and graphite fluoride, and at leastone solid lubricant is selected from among molybdenum disulfide,tungsten disulfide, boron nitride, calcium fluoride, talc and magnesiumsilicate mineral powders.